It is widely accepted that children who fulfill the DSM-III-R criteria for Attention Deficit- Hyperactivity Disorder (ADHD) are a heterogeneous group, but reliable methods do not exist for defining identifiable homogenous subgroups. The proposed research will develop a microcomputer-based battery of tasks which will assess several aspects of auditory and visual attention in children between 5 and 14 years of age. As a primary objective, the battery should identify those ADHD children whose functioning of neuropsychologic mechanisms of attention is significantly impaired in comparison with a normal population.Secondarily, it is aimed that of those children recognized as neuropsychologically deficient, nearly homogeneous subgroups may be identified in a way that is both statistically and clinically significant. These subgroupings will be indicators of which of the several neuropsychologic mechanisms participating in attention are to be suspected as primary deficits. Experts in educational psychology, psychological measurements and biostatistics will participate in the design and final critical assessment of the attention battery, and an informal trial will be carried out on about 20 children in Phase I to assess the feasibility of norming and validating the attention battery with controlled populations in Phase II.